System for dampening return motion of a carriage

ABSTRACT

Upon the travel of a carriage, such as is used in a teleprinter, from a starting position across a page to print a line of type, a dashpot plunger is retracted from a cylinder to form a fluid cushion in the cylinder. As the carriage travels further and further across the page, a latch is positioned so that a series of abutment steps on the latch are sequentially moved into engagement with the dashpot plunger. This permits limited further movement of the dashpot plunger out of the cylinder in a series of steps, thereby enlarging the fluid cushion as the carriage return distance increases. Upon receipt of a &#39;&#39;&#39;&#39;carriage-return&#39;&#39;&#39;&#39; signal, when a new line is to be started, the carriage is returned from the final printing position to the starting position. As the carriage returns to the starting position, the dashpot plunger is engaged and forced back into the dashpot cylinder, against the fluid cushion, to dampen the return motion of the carriage. The position-responsive latch structure provides a variable stroke dashpot system, with successively larger fluid cushions available for increased carriage-return distances, so as to provide for smooth return of the carriage with a minimum of bounce, regardless of carriage-return distance and velocity.

I nited States Patent 1191 Riley 1 Jan. 21, 1975' SYSTEM FOR DAM PENING RETURN MOTION OF A CARRIAGE [75] Inventor: Arthur F. Riley, Chicago, Ill.

[73] Assignee: Teletype Corporation, Skokie, 111.

[22] Filed: Feb. 14, 1974 21 Appl. No.: 442,511

52 us. c1 197/64, 197/177, 197/183 Primary ExaminerEdgar S. Burr Assistant Examin-erR. T. Rader Attorney, Agent, or FirmJ. L; Landis 57 ABSTRACT Upon the travel of a carriage, such as is used in a teleprinter, from a starting position across a page to print a line of type, a dashpot plunger is retracted from a cylinder to form a fluid cushion in the cylinder. As the carriage travels further and further across the page, a

latch is positioned so that a series of abutment steps on the latch are sequentially moved into engagement with the dashpot plunger. This permits limited further movement of the dashpot plunger out of the cylinder in a series of steps, thereby enlarging the fluid cushion as the carriage return distance increases. Upon receipt of a carriage-return signal, when a new line is to be started, the-carriage is returned from the final printing position to the starting position. As the carriage returns to the starting position, the dashpot plunger is engaged and forced back into the dashpot cylinder, against the fluid cushion, to dampen the return motion of the carriage. The position-responsive latch structure provides a variable stroke dashpot system, with successively larger fluid cushions available for increased carriage-return distances, so as to provide for smooth return of the carriage with a minimum of bounce, regardless of carriage-return distance and vel'ocity.

5 Claims, 4 Drawing Figures PATENTEDJANZI I915 3.361.513

' sum 2 or 2 o 400 444 23s 44s BACKGROUND OF THE INVENTION This invention relates to an improved system of dampening the return motion of carriages, such as are used in teleprinters, and more particularly to a variable-stroke dashpot assembly where the volume of the fluid cushion in the dashpot cylinder is increased as the carriage return distance increases.

In various conventional teleprinter systems, the carriage-return motion is dampened and terminated by a dashpot assembly. One type of printer and carriagereturn mechanism with which this invention may be used is disclosed in T. A. Przysiecki US. Pat. No. 3,243,031, herein incorporated by reference. The kinetic energy which must be absorbed by the dashpot assembly varies with the speed of movement of the carriage on return, with the speed being dependent on the distance through which the carriage has traveled before a return signal is received. Difficulty has been experienced, particularly in wide-platen printers, in that when the dashpot assembly is adjusted so as to properly accommodate the forces generated by a relatively longdistance carriage return, to absorb a relatively large amount of kinetic energy, such an adjusted dashpot assembly causes too great or sudden a braking action for a short carriage return, which causes pneumatic bounce of the carriage. Conversely, when the dashpot assembly is adjusted to properly accommodate a short carriage return, to absorb relatively small amounts of kinetic energy, then such an adjusted dashpot provides too light or weak a braking action for a long carriage return, which causes mechanical bounce of the carriage.

SUMMARY OF TI-IE INVENTION a processing operation such as printing. In accordance with certain features of the invention, an escapement device or variable stop is' interposed into the path of a conventional dashpot plunger as it extends from a cylinder on carriage advance. The stop is arranged and selectively positioned in the path of the plunger so that the plunger is extended increased distances corresponding to increased increments of carriage travel. This correspondingly increases dashpot volume, and dampening effect, for increased distance of carriage travel so as to minimize bounce on carriage return.

Other objects, advantages and features of the invention are discussed in connection with the following detailed description of a preferred embodiment of the invention, taken together with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a front elevation of a carriage advancing and return mechanism, including a dampening system according to the preferred embodiment of this invention.

FIG. 2 is a plan view of a portion of the assembly shown in FIG. I, along line 22 of FIG. 1.

FIG. 3 is an enlarged front view of a portion of the mechanism shown in FIG. 1, shown at a later stage of operation.

FIG. 4 is a view similar to FIG. 3. at a further stage.

DETAILED DESCRIPTION Referring now in detail to the drawings, and particularly to FIGS. 1 and 2, this invention relates to an improved dampening mechanism, or variable-stroke dashpot assembly 400. In the preferred embodiment illustrated, the dashpot assembly is incorporated into a teleprin'ter including a carriage 72, a spacing assembly 401 and a carriage-return assembly 402 of the type disclosed in the Przysiecki US. Pat. No. 3,243,031, and as utilized in the standard TELETYPE Model 28, 35 and 37 printers. While the Przysiecki patent is specifically concerned with a special Braille printer, the carriage-return mechanism can be used with many types of printers, or with similar devices having movable carriages of such type. Where possible, like parts herein have been numbered in accordance with the numerals of that patent. In particular, numerals below 300 refer to corresponding structures enumerated in the Przysiecki patent, while those beginning with 400 relate particularly to this application. Background Structure The spacing assembly 401 moves a carriage 72 in conventional fashion step-by-step to the right from an initial or starting position shown in FIG. 1, across a platen 403, for printing a message on a page disposed between the carriage and platen. When the'line has been completed, a carriage-return" signal is received and the assembly 402 operates to return the carriage 72 to its starting or home position preparatory to printing of the next line. As described in detail in the Przysiecki patent, the spacing assembly 401 includes a shaft 221 having a pair 'of eccentrics 222 and 223 mounted thereon to drive a pair of spacing pawls 224 and 225. The pawls are biased by springs 226 (one shown) to engage with teeth 227 of a spacing ratchet 228 which is rotatably mounted on astud shaft 229 and is secured .to a winding drum 230 so that reciprocation of the pawls 224, 225 turns the winding drum 230 step-bystep in a clockwise direction as viewed in FIG. 1.

The drum 230 is secured to a pair of parallel cables 231 which are also fixed to the carriage 72 so that the stepwise rotation of the drum 230 causes linear advancement or stepping .of the carriage from left-toright. The spacing pawls 224, 225 reciprocate alterpulleys 234435) so that clockwise rotation of the,

winding drum 230 causes corresponding rotation of the spring drum 233 as the carriage 72 is advanced by the winding drum, and so that counterclockwise rotation of the spring drum 233 causes corresponding rotation of the spacing drum 230'and return movement of the carriage 72.

The spring drum 233 is freely rotatable about a shaft 236, and has aconventional clock spring 237 attached to its inner periphery and to the shaft 236, so that the spring is wound up as the drum 233 rotates in the clockwise direction during carriage advance. The clock spring 233 is wound to store energy which will subsequently be used for carriage return in known fashion.

When the spacing drum 30 first starts rotating on carriage advance, clockwise from the position in FIG. 1 toward the FIG. 3 position, a pawl-restoring lever 249 and a dashpot-actuating roller 250 turn with the drum 230 and are retracted from their home positions, as described in the Przysiecki patent, in preparation for the next carriage-return step discussed hereafter.

Upon the receipt by the printer of the carriage-return signal, an electromagnet (not shown in this application) operates a mechanical linkage structure shown in FIG. 4 of the Pryzysiecki patent to disengage the pawls 224 and 225 from the teeth 227 of drum 230, thus freeing the drum 230 for return movement (in the counterclockwise direction) under the control of the clock spring 237. At the same time, a latch (not shown herein) mounted on a stud pivot 277 functions to hold the pawls 224-225 out of engagement with the drum 230 until the carriage has reached the home position, at which time the pawl-restoring lever 249 returns to the FIG. I position and engages a driving member 278 mounted on the shaft 277, to release the pawl-holding latch and return the carriage-return structure to its initial position for the next line.

In addition, as the winding drum 230 turns counterclockwise, back toward its initial position, the dashpotactivating roller 250, mounted for rotation therewith, engages a cam face 285 formed on an arm 286 of a dashpot piston rod or plunger 287, to drive the plunger 287 back into the dashpot cylinder 288 against the fluid cushion therein, to cushion or dampen the return motion of the carriage 72 in known fashion. As described in the Przysiecki patent, the cam face 285 is so shaped as to generally increase the force with which the plunger 287 is driven into the cylinder 288 as the plunger is driven by the roller 250. The plunger 287 is biased to the left, in conventional fashion, by a dashpot spring 289 so that the, plunger 287 is withdrawn from the cylinder 288 on carriage advance, as the winding drum 230 turns clockwise from the FIG. 1 position toward'the FIG, 3 position, so as to move the plunger 287 to a leftward position in preparation for the next return operation.

As previously mentioned, the roller 250 guides the plunger retraction during the first few characters of each line of a message after which the roller 250 loses control. In the prior-art structures, as typified by the Przysiecki patent, the spring 289 then pulls the plunger -to a retracted, stop position where the right end wall 406 of a slot 407 in the plunger body engages a fixed stopping pin or shaft 408, where the plunger remains positioned until the roller 250 drives it back into the cylinder 288. The left-end wall 409 (FIGS. 3 and 4) of the slot 407 serves as a stop for carriage return, and limits the stroke of the plunger 287.

In connection with the carriage-return system, which as previously mentioned is driven by the clock spring 237 wound between the spacing drum 233 and the shaft 236, an initial adjustment in spring tension may be effected for imparting predetermined torque to the spring drum 233 to apply a desired initial tension to the cable 23]. Referring to the left side of FIG. 1, this is accomplished by a ratchet wheel 410, mounted on the shaft 236 and a pawl 411, pivoted at 412, which cooperates in a known manner with teeth 413 of the ratchet wheel 409 to permit counterclockwise rotation of the ratchet wheel 409. In practice, the ratchet wheel 409 is manually rotated in a counterclockwise direction prior to the start of a printing operation, to wind the clock spring 237 to a degree sufficient to exert the desired initial torque on the spring drum 233. Dampening Mechanism 400 As previously mentioned, this invention relates to an improved dashpot dampening mechanism 400, which is preferably used with the prior known carriage assembly just described. As will be apparent, this system could also be used in other assemblies where a dashpot assembly such as 287-288 is used to dampen return of a heavy member such as carriage 72, where the carriage must travel variable distances in an operation such as printing.

In accordance with this invention, in a typical specific embodiment illustrated, the dampening mechanism 400 includes a cam 414 fixed to the winding drum 230 and having a set of six camming surfaces 416421 of increasingly larger radii (as one proceeds around the cam 414 in a counterclockwise direction from the innermost cam surface 416). The camming surfaces sequentially act on a cam follower 423 at predetermined angles of rotation of the drum 230, as it rotates in a clockwise direction (corresponding to increments of carriage advance), to pivot the cam follower 423 away from the cam 414. The follower 423 is pivotably mounted on the stud shaft 277 previously described, and is urged against the cam 414 by a spring 424. The follower 423 is connected to a latching arm 427, which is also pivoted on the shaft 277 so that the latching arm 427 pivots together with the cam follower 423.

The latching arm 427 is formed with a series of five abutment stops or steps 429-433, which can be moved sequentially into and out of the path-of movement of a boss 436 formed near the outer (left) end of the dashpot plunger 287. As the carriage 72 advances beyond each of a series of preset distances across the page, the abutment steps are sequentially moved into the path of the boss 436, so that the dashpot plunger 287 moves step-by-step to the left as the carriage movement proceeds. This step-by-step movement, or escapement, is generated as the cam follower 423 is sequentially pivoted away from the cam 414 by the camming surfaces 416-421 as the winding drum 230 rotates progressively further, as a direct function of carriage travel.

When the dashpot plunger 287 is first released by the roller 250, the cam follower 423 rides on the innermost camming surface 416 and the first abutment step 429 is in line with the path of the boss 436, as illustrated in FIG. 3. The boss 436 is urged into engagement with the first step 429 by the dashpot spring 289. Movement of the dashpot plunger 287 and piston 444, out of the cylinder 288, permits a fluid, normally air from the atmosphere, to enter the rear of the cylinder, through a valve 445 having a port 446. This generates an initial fluid cushion in the dashpot cylinder 288. This initial fluid cushion is selected to be of sufficient volume V to dampen or cushion the return motion of the carriage to a desired degree. Thus, the kinetic energy generated by the return motion of the carriage from a position between its starting position and a predetermined first position, is absorbed by the fluid cushion V As the winding drum 230 rotates beyond this first position to move the carriage past the first predetermined position, the second camming surface 417 pivots the cam follower 423 one step in a counterclockwise direction, to pivot the latching arm 427 one step in a counterclockwise direction. This shifts the first abutment step 429 upward and out of the path of the boss 436, while positioning the following or second step 430 in the path of the boss for a prescribed period set by the arc length of the camming surface 417 in accordance with a desired carriage position. The dashpot plunger 287 then moves one further step out of the cylinder, which further enlarges the fluid cushion in the cylinder 288. This fluid cushion is also set so as to dampen the faster return motion of the carriage 72 to its initial position, without appreciable pneumatic or mechanical bounce being imparted to the carriage upon its return.

Further rotation of the winding drum 230 moves the carriage past a predetermined second position, set by the end of the second camming surface 417, then to a third position, and so on through the six steps set by the camming surfaces 416-421, the first five of which correspond to the five abutment steps 429-433. This in turn, results in each abutment step in turn being moved into the path of the boss 436 to further increase the dashpot volume from V (FIG. 3) to V (FIG. 4) to accommodate successively faster carriage return speeds generated by increased return distances, as powered by the clock spring 237.

After the final abutment step 433 is displaced out of the path of the boss 436 by the last cam surface 421 (just after the time shown in FIG. 4), the plunger 287 moves further to the left to its last stop, where the inner end 4060f the slot 407 engages the pin 408 (as in the Przysiecki patent). This is the final position, used for a full line of printing, where the carriage return distance and thus speed are maximum. For all distances of carriage-traveL-the dashpot air volumes are set to minimize bounce; that is, in each instance, the volume of the fluid cushion, when forced through the port 446 as the moving carriage drives the piston 444 back into'the cylinder is set to dampenor absorb smoothly the return motion of the carriage. Thus a variable-stroke dash pot is provided, whose volume is a predetermined function of carriage-return distance, as set by the contours of the cam surfaces 415421, and the lengths of the steps 429-433.

When the carriage-return signal is received, and the spring drum 233 begins returning the carriage 72 to the initial position, the winding drum 230 follows the spring drum 233, and thus rotates in a counterclockwise direction toward its initial position (FIG. 1). At

this time, the camming surfaces 421 through 416 sequentially move past the cam follower 423, but the follower does not engage the camming surfaces at this time because the spring 424 urges the latching arm 427 downward (clockwise) against the boss 436 of the dashpot'plunger 287, regardless of the stop position of the plunger when the return signal was received. The combination of the dashpot spring 289 and the stopmember spring 424 maintain both the plunger 287 and the stop member 427 in their previously set positions, based on carriage travel, until the dashpot-actuating roller 250 rotates back to the position where it picks up the dashpot arm 286 andthereafter returns the plunger to its initial position in the dashpot cylinder, as previously described. As the plunger returns home, the boss 436 moves out from under the latching arm 427, thereby allowing the spring 424 to pivot both the latching arm and the cam follower 423 clockwise until the follower again engages the cam 414.

Simultaneously with the return of the dashpot roller 250 to the position shown in FIG. 1, the lever 249 engages the driving member 278 to release the spacing pawls 224 and 225, which then are again urged by the springs 226 into engagement with the teeth 227 of the spacing ratchet 228. The spacing assembly 401, carriage-return assembly 402, and dampening mechanism 400 have thus been returned to their initial positions in preparation for printing of the next line across the platen 403.

Operation To review the main points of operation, particularly those pertaining to the variable-stroke dashpot system 400 of this invention, preparatory to printing the clock spring 237 is manually prewound to a desired initial tension and the dashpot valve 245 is set to adjust the port 446 for the midrange of expected operations. As in the Przysiecki patent and in the standard Model 28, 35 and 37 printers, when a start signal is received from the telegraph line, the drive pawls 224 and 225 step the carriage 72 across the platen 403 to print a line of a message, and the carriage continues to step until a carriage-return signal is received to return the carriage promptly to its initial position. As is conventional, the line length (carriage travel) for any particular line may be anything from 1 or 2 characters up to the full width of the line, which may be as much as 14 inches in the so-called wide-platen terminals.

As the carriage 72 steps across the page, the spring drum 233 turns to wind the clock spring 237.- The further the carriage travels beforethe return signal is received, the tighter the clock spring is wound before'release, and the faster the carriage travels at the end of thereturn stroke. The variable-stroke dashpot system 400 serves to equalize the effects of variable carriage speed (and thus kinetic energy) at the end of the return stroke by increasing the dashpot volume, and thus the cushioning or dampening effect, in proportion to carriage travel, so as to return the carriage promptly to the home position with a minimum of bounce in all cases.

As the spacing drum 230 first begins to turn, the dashpot-activating roller 250 turns clockwise with the drum and the dashpot plungerv 287 follows the withdrawing roller 250, as in the prior mechanisms, until the roller 250 travels out from under the arm 286 (shortly prior to the position depicted in FIG. 3).

In accordance with this invention, as the roller 250 loses control over the plunger 287, the plunger is substantially immediately engaged by the first stop or abutment step 429 of the latch 427, instead of being unrethe first step 429 engages-the boss 436 on the plunger and 433 are programmed by the corresponding cam arcs 418, 419, and 420 to increase the piston volume in further steps to V (FIG. 4), as the plunger travels further outward following the contour of the latch 427. If the particular line of type requires carriage travel to a position approaching the maximum limit (end of the line), the final cam surface 421 pivots the latch 427 to a position above and riding on the boss 436, to provide a final position as in the prior art, where the stopping edge 406 of the slot 407 in the plunger engages the pin 408. This final step provides a maximum cylinder volume V when the clock spring 237 has been wound to the maximum degree and the carriage-return distance and velocity are maximum.

In a relatively simple example of the invention, the six cam steps 417-421 could be of equal length, and the abutments steps 429-432 of equal depth, so as to evenly divide the carriage travel distance (after the roller 250 loses control) into six equal increments with progressively increasing dashpot volumes from V to V However, any number of cams and steps can be used for maximum return efficiency, and the timing and displacement can be programmed at varying intervals depending on the circumstances and observed results as to carriage travel, the properties of the clock spring 237 and of dashpot operation, a preferred example of which programming is described hereafter.

When the carriage return signal is generated, the clock spring 237 returns the carriage 72 rapidly to its home position, which rotates the drums 233 and 230 back to their initial positions as previously described. At this time, the plunger 287 temporarily remains in its previously set extended position at the time the return signal was received, due to the coaction of the springs 289 and 424. However, as the spacing drum 230 approaches its starting position, the roller 250 again engages the plunger arm 286, generally as in the Przysiecki patent, and thus forces the piston 444 back into the dashpot cylinder 288, as is well known in this type of dashpot. The corresponding, variable air cushion V V in the cylinder absorbs the kinetic energy of the relatively heavy carriage, and thus dampens the return movement such that the carriage decelerates rapidly to a relatively smooth stop. As previously noted, with the present invention, thedashpot return stroke is variable and is preset by the discrete steps set by the latch 427, in accordance with the carriage position at the time the return stroke is initiated. The volume V V, of fluid in the dashpot cylinder is thus increased in accordance with the carriage-return distance, and thus with the speed and kinetic energy of the carriage on return. In this manner, pneumatic and mechanical bounce to the carriage are greatly reduced or eliminated.

By mechanical bounce is meant a condition where the piston advance is too rapid (the air cushion does not provide sufficient dampening) and the left end wall 409 of the plunger slot 407 strikes the pin 408 sharply on return, causing the carriage to rebound. By pneumatic bounce is meant a situation where the air cushion is too resistive; that is, the air does not escape rapidly enough through the port 446, and the piston tends to rebound against the air cushion. The present invention, with its variable stroke dashpot 400 based on carriage position is designed to minimize both types of bounce and provide smooth carriage return over a wide range of positions and speeds.

In one specific embodiment preferred for a wideplaten printer 14 inches or characters maximum), six stops are used, programmed with decreasing length cam arcs as follows:

This arrangement provides optimum damping in this particular system, with the dashpot volume programmed to be stepped more and more frequently as the carriage travels farther and farther from home, because of the increasing return impact velocities generated as the carriage 72 travels further and the clock spring 237 is wound tighter.

While one specific embodiment of the invention has been described in detail above, it will be obvious that various modifications may be made in the specific details described without departing from the spirit and scope of the invention.

What is claimed is:

1. In combination with a system for dampening return movement of a carriage, of the type wherein the carriage is advanced a variable distance from a home position in a processing operation and then is driven back to the home position with a velocity that is an increasing function of the distance of carriage travel, and wherein the carriage-return movement is dampened by a dashpot system ofthe type having a dashpot plunger which is biased to extend out of a dashpot cylinder on carriage advance, and an actuating member which moves in synchronism with the carriage and engages a portion of the plunger near the end of the return stroke of the carriage to force the plunger back into the cylinder and thus dampen the return movement of the carriage, an improved variable-stroke dampening mechanism which comprises:

an escapement device having a series of stops for engaging the dashpot plunger as it extends from the cylinder on carriage advance and limiting the travel of the plunger to a series of fixed stop positions; and means for actuating the escapement device in accordance with the distance of carriage travel so that the plunger is extended increasing distances corresponding to increasing increments of carriage travel, and so that the volume of the fluid in the dashpot increases as carriage travel increases to provide increased dampening for increased distances of carriage return. 2. A dampening mechanism as recited in claim 1, wherein:

the escapement device comprises a pivoted latching arm having a stepped surface, the dashpot plunger having a boss positioned to be intercepted and stopped in sequence by each of the steps on the latching arm; and the actuating means comprises a rotary cam mounted for rotation in synchronism with carriage travel, and a cam follower biased against the cam and connected to the latching arm so as to pivot the latch ing arm and serially present the steps to the boss as the carriage travels increasing distances.

3. A dampening mechanism as recited in claim 2, wherein the cam portions are of progressively decreasing arc length as the cam rotates upon carriage travel, so that successive stops are actuated more frequently as the carriage travels farther from home and the dashpot volume thereby increases more rapidly toward the maximum limit of carriage travel.

4. A carriage return mechanism as recited in claim 2, for a teleprinter, of the type wherein the carriage is connected to both a winding drum and a return drum mounted on a frame so that rotation of the winding drum causes carriage advance, the return drum having a clock spring which is wound in accordance with the length of carriage travel across a page before a return signal is received, the clock spring serving to power return movement of the carriage with a terminal velocity that is an increasing function of the distance of carriage travel, the winding drum reversing rotation and following the rotation of the return drum on carriage return, a dashpot-actuating roller being mounted for rotation with the winding drum and arranged to engage an arm on the dashpot plunger near the end of carriage return to force the plunger back into the dashpot cylinder, further characterized in that:

the cam is mounted for rotation with the winding drum and is formed with surface arcs of increasing radius in the direction of rotation on carriage advance; and the cam follower comprises an arm pivotally mounted on the frame so as to follow the surface of the cam, and a spring for urging the follower arm 2 against the cam, the spring also serving to urge the latching arm against the boss on the dashpot plunger so as to temporarily hold the plunger in the extended position it occupied on receipt of the carriage-return signal until the dashpot-actuating roller engages the arm on the dashpot plunger, after which the cam follower is again free to follow the cam surface and the latching-arm correspondingly returns to its first stopping position.

5. In combination with a process for dampening return movement of a carriage, of the type wherein the carriage is advanced a variable distance from a home position in a processing operation and then is driven back to the home position with a velocity that is an increasing function of the distance of carriage travel, and wherein the carriage-return movement is dampened by a dashpot system of the type having a dashpot plunger which is biased to extend out of a dashpot cylinder on carriage advance, and an actuating member which moves in synchronism with the carriage and engages a portion of the plunger near the end of the return stroke of the carriage to force the plunger back into the cylinder and thus dampen the return movement of the carriage, an improved variable-stroke dampening process turn. 

1. In combination with a system for dampening return movement of a carriage, of the type wherein the carriage is advanced a variable distance from a home position in a processing operation and then is driven back to the home position with a velocity that is an increasing function of the distance of carriage travel, and wherein the carriage-return movement is dampened by a dashpot system of the type having a dashpot plunger which is biased to extend out of a dashpot cylinder on carriage advance, and an actuating member which moves in synchronism with the carriage and engages a portion of the plunger near the end of the return stroke of the carriage to force the plunger back into the cylinder and thus dampen the return movement of the carriage, an improved variable-stroke dampening mechanism which comprises: an escapement device having a series of stops for engaging the dashpot plunger as it extends from the cylinder on carriage advance and limiting the travel of the plunger to a series of fixed stop positions; and means for actuating the escapement device in accordance with the distance of carriage travel so that the plunger is extended increasing distances corresponding to increasing increments of carriage travel, and so that the volume of the fluid in the dashpot increases as carriage travel increases to provide increased dampening for increased distances of carriage return.
 2. A dampening mechanism as recited in claim 1, wherein: the escapement device comprises a pivoted latching arm having a stepped surface, the dashpot plunger having a boss positioned to be intercepted and stopped in sequence by each of the steps on the latching arm; and the actuating means comprises a rotary cam mounted for rotation in synchronism with carriage travel, and a cam follower biased against the cam and connected to the latching arm so as to pivot the latching arm and serially present the steps to the boss as the carriage travels increasing distances.
 3. A dampening mechanism as recited in claim 2, wherein the cam portions are of progressively decreasing arc length as the cam rotates upon carriage travel, so that successive stops are actuated more frequently as the carriage travels farther from home and the dashpot volume thereby increases more rapidly toward the maximum limit of carriage travel.
 4. A carriage return mechanism as recited in claim 2, for a teleprinter, of the type wherein the carriage is connected to both a winding drum and a return drum mounted on a frame so that rotation of the winding drum causes carriage advance, the return drum having a clock spring which is wound in accordance with the length of carriage travel across a page before a return signal is received, the clock spring serving to power return movement of the carriage with a terminal velocity that is an increasing function of the distance of carriage travel, the winding drum reversing rotation and following the rotation of the return drum on carriage return, a dashpot-actuating roller being mounted for rotation with the winding drum and arranged to engage an arm on the dashpot plunger near the end of carriage return to force the plunger back into the dashpot cylinder, further characterized in that: the cam is mounted for rotation with the winding drum and is formed with surface arcs of increasing radius in the direction of rotation on carriage advance; and the cam follower comprises an arm pivotally mounted on the frame so as to follow the surface of the cam, and a spring for urging the follower arm against the cam, the spring also serving to urge the latching arm against the boss on the dashpot plunger so as to temporarily hold the plunger in the extended position it occupied on receipt of the carriage-return signal until the dashpot-actuating roller engages the arm on the dashpot plunger, after which the cam follower is again free to follow the cam surface and the latching arm correspondingly returns to its first stopping position.
 5. In combination with a process for dampening return movement of a carriage, of the type wherein the carriage is advanced a variable distance from a home position in a processing operation and then is driven back to the home position with a velocity that is an increasing function of the distance of carriage travel, and wherein the carriage-return movement is dampened by a dashpot system of the type having a dashpot plunger Which is biased to extend out of a dashpot cylinder on carriage advance, and an actuating member which moves in synchronism with the carriage and engages a portion of the plunger near the end of the return stroke of the carriage to force the plunger back into the cylinder and thus dampen the return movement of the carriage, an improved variable-stroke dampening process which comprises: successively interposing a series of stops into the path of the dashpot plunger as it extends from the cylinder so as to limit the travel of the plunger to a series of stop positions arranged so that the plunger is extended increasing distances corresponding to increasing increments of carriage travel, and so that the volume of the fluid in the dashpot increases as carriage travel increases to provide increased dampening for increased distances of carriage return. 